1. Field of the Invention
The present invention relates to fiber optic communications. More particularly, the present invention relates to a terminus to provide an orderly termination of a fiber optic cable, and to structures incorporating one or more of the termini, such as a connector, jumper, or attenuator.
2. Description of the Related Art
It is known in the background art, that a fiber optic cable may be cut and terminated for connection to a connector, jumper or attenuator, or other such structure. A typical termination includes a ferrule having a central bore passing through a center thereof. A length of optical fiber is exposed at the end of the cut fiber optic cable. The optical fiber is passed through the central bore in the ferrule and cut flush with the end of the ferrule. An epoxy secures the optical fiber within the central bore, and the cut end of the optical fiber is polished, along with the end of the ferrule, to finish the termination.
There was an appreciation in the background art that such a typical termination was unsuitable for use in harsh environments which are prone to vibration, such as in an aircraft. Since the optical fiber extended to the end of the ferrule and made physical contact with a receiving structure, the optical fiber was susceptible to damage (e.g. small stress cracks) when vibrated. U.S. Pat. No. 6,074,100, which is herein incorporated by reference, addressed this physical contact drawback associated with the typical termination.
FIGS. 17-21 illustrate the terminus of U.S. Pat. No. 6,074,100. In FIG. 17, the fiber optic cable 208 is stripped to remove and expose several sheaths of cable material. The stripped end of the fiber optic cable 208 includes a central optical fiber 212, a silicon buffer 214 disposed about the optical fiber 212, an inner jacket 216 enveloping the silicon buffer 214, a strengthening member 218 comprising a braided or woven fiber, e.g., a polyamide fiber such as Kevlar®, wrapped about the inner jacket 216, and an outer jacket 220 enveloping the strengthening member 218.
In FIG. 18, the stripped end of the fiber optic cable 208 is prepared for bonding to a ferrule assembly 222. The ferrule assembly 222 includes a rigid ferrule 224 and an aft body or sleeve 226 circumscribing and bonded to an end portion of the ferrule 224. More specifically, the rigid ferrule 224 defines an external face surface 228, a central bore 230 and an internal end 232, and the aft body 226 comprises a cylindrical inner bore 234 and a tapered end 236 defining a cylindrical outer surface 238. The ferrule 224 is fabricated from a ceramic, such as zirconia, and the aft body 226 is fabricated from stainless steel.
In preparation for bonding, a bead or ring of bonding adhesive 240 is applied to the outer surface 238 of the aft body 226, corresponding to region A, and a layer of bonding adhesive 242, corresponding to region B, is applied to the optical fiber 212 and inner jacket 214. The bonding adhesives 240, 242 in regions A and B are the same and, furthermore, are selected such that the Glass Transition Temperature (TG) is greater than the maximum temperature anticipated in the operating environment of the terminus. Prior to bonding, the strengthening members 218 are folded rearwardly over the outer jacket 220. A shrink tubing 244, which will subsequently overlay the strengthening member 218, is used to temporarily preposition the strengthening member 218 over the outer jacket 220.
In FIG. 19, the stripped end of the fiber optic cable 208 is inserted within the ferrule assembly 222 such that the optical fiber 212 passes through the ferrule bore 230 and the inner jacket 214 abuts the internal end 232 of the ferrule 224. Next, the shrink tubing 244 is slid rearwardly (shown in phantom) to release the strengthening member 218 which is then folded over the cylindrical outer surface 238 of the aft body 226. As such, the ring of bonding adhesive 240 in region A contacts and impregnates the strengthening member 218. The shrink tubing 244 is then moved forwardly such that it overlays the strengthening member 218 and the outer jacket 220. During a curing process, the adhesive 240 is solidified and the shrink tube 244 contracts. After the curing process, the end of the optical fiber 212 is cleaved in close proximity to the external face surface 228 of the ferrule 224, as illustrated in FIG. 19.
Then, various sanding or polishing operations are preformed in order to recess the cut end of the optical fiber 212 below the external face surface 228 of the ferrule 224, as illustrated in FIGS. 20 and 21. Specifically, the end profile 250 is characterized by the optical fiber 212 defining an end surface 252 which is recessed or undercut relative to the face surface 228 of the ferrule 224 (as best shown in FIG. 20). The end surface of the optical fiber 212 is at least the combination of the light-carrying core 212CO and its surrounding cladding 212CL.
By the arrangement of FIGS. 17-21, U.S. Pat. No. 6,074,100 provides a fiber optic cable termination more suitable for use in a demanding operational environment prone to vibration. By recessing the optical fiber termination 252 to a point within the ferrule end 228, the optical fiber was no longer in direct physical contact with a light transmission/reception structure (e.g., another optical fiber end or detector lens) and hence was less susceptible to damage (e.g., cracks in the optical fiber).